Admirality List of Radio Signals Volume 5 is a publication published by The United Kingdom Hydrographic Office. It contains a lot of up to date and well structured information about GMDSS:
(Hungarian version goes here)

• Worldwide communication requirements for distress, search and rescue,
• The only SOLAS compliant guide for GMDSS published in English,
• Colour diagrams depicting worldwide operational DSC ranges,
• Essential information for GMDSS students,
• Easily updated from weekly Admirality Notices for Mariners,
• Revised annually.